1. Field of the Invention
This invention relates to a coating press apparatus for coating a first and second side of a press web formed in a forming section of a papermaking machine. More specifically, this invention relates to a coating press apparatus for applying a coating onto the respective sides of a paper web.
2. Information Disclosure Statement
In the past, printed flyers and the like have been printed on lightweight coated papers. However, due to the relatively high cost of providing coaters for coating a dried, or semi-dried, paper web and further because of the cost of the coating material, various proposals have been set forth in an attempt to provide a low cost, paper or board having surface characteristics suitable for printing thereon.
In the prior art, clay has been added in the headbox in order to enhance the printability of the resultant web. However, when clay, or other mineral additives, are included in the headbox, there exists a tendency for these fines to become less dense towards the respective surfaces of the web during web formation. Therefore, the additive content is relatively high at the middle of the web thickness (or caliper) where the coating substance is not required whereas the amount of coating substance present at the surface to be printed is relatively small.
In an attempt to increase the coating, or ash, content which is normally in the order of 9% to a satisfactory printing content of 20%, it has been found necessary to increase the quantity of clay, talc, calcium carbonate or the like added to the headbox to approximately 50% of the solids content of the stock. From the foregoing, it is apparent that much of the additive added is lost during the dewatering process and the production of a 20% ash content paper is relatively costly.
In an attempt to enhance the application of a coating substance to the respective surfaces of the web, U.S. Pat. No. 3,146,159 to Muggleton and assigned to Combined Locks Paper Company, teaches the application of a layer of clay to the press roll such that this layer is transferred to the formed web.
Although the aforementioned proposal of U.S. Pat. No. 3,146,159 reduces the amount of clay required to produce a printable web, problems have been experienced in the application of the layer of clay at high speeds. U.S. Pat. No. 3,146,159 discloses a method involving applying the layer of clay by an applicator roll initially rotating at the same speed as the press roll but as the press roll increases in rotational speed, the speed of the applicator roll is reduced relative to the speed of the press roll thereby avoiding splashing of the applied coating. Whereas the aforementioned proposal is relatively successful with production speeds of 1000 fpm, serious problems have been experienced when attempting to apply a coating, or clay layer, at current speeds which approach 4000 or more fpm.
The present invention seeks to overcome the aforementioned problem by providing a short-dwell coater for applying a layer of coating substance directly to a smooth surface of a press roll such that the layer is transferred during passage of the pressed web through a first nip defined by the press roll and a first backing roll. The present invention applies the first layer of coating substance to the web that has previously passed through an upstream press nip. Therefore, the present invention provides a coating press apparatus that overcomes the aforementioned inadequacies of the prior art proposals and provides a coating press which makes a significant contribution to the papermaking art.
Another object of the present invention is the provision of a coating press apparatus in which a first short-dwell coater applies a coating substance directly to a smooth imperforate surface of a first press roll upstream relative to a first nip defined by the first press roll and a first backing roll.
Another object of the present invention is the provision of a coating apparatus in which a second short-dwell coater is disposed downstream relative to the first nip for applying a smooth and even second layer of a coating substance to the second side of the web so that the web exhibits a higher coating content at the first and second side surfaces thereof than the coating content between the first and second sides thereby enhancing the printability of the resultant web.
Another object of the present invention is the provision of a coating press which includes a second press roll and a second backing roll defining therebetween a second nip for the passage therebetween of a first felt and the web. The second nip is disposed upstream relative to the first nip and a second felt extends through the second nip such that the web is disposed between the first and second felts during passage through the second nip.
Another object of the present invention is the provision of a coating press apparatus in which the first short-dwell coater includes a doctor which is disposed upstream relative to the first nip for cleaning the imperforate first surface prior to the coating of the surface with the first layer. The first short-dwell coater also includes an applicator which is disposed between the doctor and the first nip for applying the first layer to the imperforate surface. Additionally, the first short-dwell coater includes a metering blade or rod which is disposed between the applicator and the first nip for smoothing the first layer before the first layer is brought into physical contact with the first side of the web.
Another object of the present invention is the provision of a coating press apparatus which includes a third backing roll which is disposed downstream relative to the first nip, the third backing roll cooperating with the first press roll such that a third nip is defined between the third backing roll and the first press roll so that the web is pressed during passage through the third nip with the second side of the web facing towards the third backing roll.
Another object of the present invention is the provision of a coating press apparatus which includes a third press roll and a fourth backing roll which cooperates with the third press roll for defining therebetween a fourth nip. A fourth felt extends through the fourth nip with the fourth felt disposed in physical contact with the first side of the web. The second short-dwell coater cooperates with the second surface of the third press roll for applying a second layer of coating substance to the second surface such that the second layer is transferred onto the second side of the web during transit through the fourth nip.
Other objects and advantages of the present invention will be apparent to those skilled in the art by a consideration of the detailed description contained hereinafter taken in conjunction with the annexed drawings.